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Introduction:

A combination of techniques has been used to examine the composition of smoke generated by landing aircraft.

A sample of dust from the undercarriage from several commercial airliners was examined with SEM/EDX (Scanning Electron Microscope/Energy Dispersive X-ray) to determine its elemental composition and also with an aerosizer/aerodisperser in order to measure the particle size spectrum. The observed size spectrum was bimodal with equal numbers of particles at peaks of aerodynamic diameter ∼10 μm and ∼50 μm. The EDX analysis suggested that the former peak is carbonaceous, while the latter consists of elements typical of an asphalt concrete runway. In the field, a scanning Lidar, in combination with optical and condensation particle counters, was deployed to obtain limits to the number concentration and size of such particles. Most of the (strong) Lidar signal probably arose from the coarser 50 μm aerosol, while respirable aerosol was too sparse to be detected by the optical particle counters.

Description:

With most of the modeling of particulate matter (PM) concentrated on emission, the smoke emitted from aircraft landing has been largely neglected, despite being clearly visible to the naked eye, while that from the modern jet engines, even on full power, scarcely visible.

When an aircraft lands, the main wheels make contact with the ground and spin up; the nose wheel drops to the ground; the brakes are then applied to bring the aircraft to a halt. The smoke that is visible is usually only released as the wheels spin up and breaks subsequently release fine aerosol as they abrade.

From mass balance calculation, we know that the amount of rubber lost per landing is substantial, with Boeing 747 loosing up to 1kg of rubber.

From the recent measurements, organic carbon and associated trace metal in the near ambient particulate matter is released as fine aerosol, but it is not understood how much of it is dispersed and how much adheres to the runway or is scattered as macroscopic fragments.

The Lidar monitoring system sensitive to sparse, coarse aerosol generated by the landing aircraft, with the point samplers struggling to resolve these particles. In sum, observations suggested that the tire aerosol is too coarse to be respirable. It consists largely of mechanically generated dust from runway surface, with very little rubber lost released as fine aerosol.

Grimm UPC particle counter, which is sensitive to ultra-fine particles, detected the engine emissions sensitively, although there were too few particles in the tire smoke to provide a strong enough signal.

In total, while emissions present in tire smoke can be of particular significance, the respirable emissions of particulate matter is relatively modest. However, health issues arising from hazardous organics from volatilized rubber can pose as a nuisance from the associated odor.